Whadda WSEDU02, Инструкция по сборке

Страница: 23 / 28

23
Required parts: Solar cell, BC557 transistor, 4K7 resistor (yellow, purple, red, gold),
470 ohm resistor (yellow, purple, brown, gold), BAT85 diode, yellow led, battery holder
for two AAA batteries, two AAA 1.2V rechargeable batteries, jumper wire.
How it works
: When the sun shines, the
voltage generated by the solar cell will be
higher than the voltage of the batteries, so a
current will flow from the solar cell to the
batteries. This current will charge the
batteries. The BAT85 diode prevents
discharging of the batteries trough the solar
cell in low light conditions. The base of the
transistor is tied to ground (
-
) by means of
the 4K7 resistor. This causes the transistor
to turn on and allows a current to flow from
the batteries trough the transistor, the led
and via 470 ohm resistor back to the
batteries. The led will turn on. However,
note that the base of the transistor is also
tied to the (+) of the solar cell, so as long as
the sun shines, the base of the transistor is
kept high enough to prevent turn
-
on of the
transistor, so the led remains off at daytime.
SOLAR CELL
BC55 7
or an ge led
R1
4K7
D1
BAT8 5
R2
47 0
C
harge
curren
t
Led current
(only at night)
Bas
e
cu
rren
t (o
nly
at
ni
ght
)